class Base:
    def __init__(self):
        super().__init__()
        print("Base initialized")


class BadMixin:
    def __init__(self):
        super().__init__()
        print("Mixin initialized")  # ❌ 忘记调用 super()


class Child(BadMixin, Base):
    def __init__(self):
        super().__init__()


Child()  # 输出: "Mixin initialized" → Base 未被初始化!
